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Millimeter Wave Inverse Pinhole Imaging

Akarsh Prabhakara, Yawen Liu, Aswin C. Sankaranarayanan, Anthony Rowe, Swarun Kumar

TL;DR

Umbra addresses the limited angular resolution of compact mmWave radars in vision-denied contexts by introducing rotating mmWave inverse pinholes to generate angular diversity from a single antenna. By modeling bidirectional pass-through and diffraction and by implementing a lightweight inverse pinhole (about $10$ g) and leveraging drone propellers as natural pinholes, Umbra achieves a measured azimuth resolution of $2.5^{\circ}$, a $5\times$ improvement over a $14^{\circ}$ baseline. The authors present the system design, a diffraction-aware imaging model, reconstruction via truncated SVD, and extensive evaluations on static scenes and natural environments up to $20$ m. The work demonstrates a practical path to high-resolution mmWave imaging with minimal RF hardware, enabling static-mount or hovering-drone perception with lower weight, power, and cost.

Abstract

Millimeter wave (mmWave) radars are popular for perception in vision-denied contexts due to their compact size. This paper explores emerging use-cases that involve static mount or momentarily-static compact radars, for example, a hovering drone. The key challenge with static compact radars is that their limited form-factor also limits their angular resolution. This paper presents Umbra, a mmWave high resolution imaging system, that introduces the concept of rotating mmWave "inverse pinholes" for angular resolution enhancement. We present the imaging system model, design, and evaluation of mmWave inverse pinholes. The inverse pinhole is attractive for its lightweight nature, which enables low-power rotation, upgrading static-mount radars. We also show how propellers in aerial vehicles act as natural inverse pinholes and can enjoy the benefits of high-resolution imaging even while they are momentarily static, e.g., hovering. Our evaluation shows Umbra resolving up to 2.5$^{\circ}$ with just a single antenna, a 5$\times$ improvement compared to 14$^{\circ}$ from a compact mmWave radar baseline.

Millimeter Wave Inverse Pinhole Imaging

TL;DR

Umbra addresses the limited angular resolution of compact mmWave radars in vision-denied contexts by introducing rotating mmWave inverse pinholes to generate angular diversity from a single antenna. By modeling bidirectional pass-through and diffraction and by implementing a lightweight inverse pinhole (about g) and leveraging drone propellers as natural pinholes, Umbra achieves a measured azimuth resolution of , a improvement over a baseline. The authors present the system design, a diffraction-aware imaging model, reconstruction via truncated SVD, and extensive evaluations on static scenes and natural environments up to m. The work demonstrates a practical path to high-resolution mmWave imaging with minimal RF hardware, enabling static-mount or hovering-drone perception with lower weight, power, and cost.

Abstract

Millimeter wave (mmWave) radars are popular for perception in vision-denied contexts due to their compact size. This paper explores emerging use-cases that involve static mount or momentarily-static compact radars, for example, a hovering drone. The key challenge with static compact radars is that their limited form-factor also limits their angular resolution. This paper presents Umbra, a mmWave high resolution imaging system, that introduces the concept of rotating mmWave "inverse pinholes" for angular resolution enhancement. We present the imaging system model, design, and evaluation of mmWave inverse pinholes. The inverse pinhole is attractive for its lightweight nature, which enables low-power rotation, upgrading static-mount radars. We also show how propellers in aerial vehicles act as natural inverse pinholes and can enjoy the benefits of high-resolution imaging even while they are momentarily static, e.g., hovering. Our evaluation shows Umbra resolving up to 2.5 with just a single antenna, a 5 improvement compared to 14 from a compact mmWave radar baseline.
Paper Structure (11 sections, 1 equation, 10 figures, 1 table)

This paper contains 11 sections, 1 equation, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. Background
  3. Related Work
  4. Umbra System Design
  5. Pinhole motion to mimic SAR
  6. mmWave Pinhole System Model
  7. Pinhole Design
  8. Practical Realization of Inverse Pinholes
  9. Implementation
  10. Evaluation
  11. Conclusion

Figures (10)

  • Figure 1: Umbra designs an inverse pinhole to image from a single antenna on a mmWave radar for static mount radars. For momentarily static use cases like a drone hovering (puller configuration, pusher configuration, thrust vectored tilt and hover), we can exploit radar illuminating through rotating propellers as natural inverse pinholes. We show Umbra's superior angular (azimuth) resolution and sharpness compared to compact radars awr.
  • Figure 2: (a) shows a simple case of antenna and target; (b) shows a synthetic aperture radar case of a moving antenna; (c) shows a pinhole and (d) inverse pinhole imaging case with a static antenna
  • Figure 3: Shows the positive impact, on (a) singular values (b) angular resolution, of bidirectional pass in contrast to unidirectional pass.
  • Figure 4: (a) shows pinhole setup. (b) & (c) contrasts singular values by varying pinhole width and pinhole's location.
  • Figure 5: (a) Shows noise in mmWave radar isn't signal dependent. (b) & (c) contrasts the singular values and angular resolution of regular pinhole and inverse pinhole respectively.
  • ...and 5 more figures